Polyether complexes of groups 13 and 14

Abstract

Notable aspects of the chemistry of complexes of polyether ligands including crown ethers, cryptands, glycols, glymes, and related polyether ligands with heavier group 13 and 14 elements are reviewed with a focus on results from 2005 to the present. The majority of reported polyether complexes contain lead(ii) and thallium(i) but recent breakthroughs in regard to the preparation of low oxidation state reagents of the lighter congeners have allowed for the generation of complexes containing indium(i), gallium(i), germanium(ii), and even silicon(ii). The important roles of ligand size, donor types, and counter anions in regard to the chemical properties of the polyether complexes is highlighted. A particular focus on the structural aspects of the numerous coordination complexes provides a rationale for some of the spectacular contributions that such compounds have made to Modern Main Group Chemistry.

Why Do Five Ga+ Cations Form a Ligand‐Stabilized [Ga5]5+ Pentagon and How Does a 5:1 Salt Pack in the Solid State?

“…To elucidate possible aggregation reactions in solution, aD OSY-NMR study in o-DFB at À20 8 8Cw ith as timulatedecho impulse sequence and including the non-reactive salt NBu 4 + [Al(OR F ) 4 ] À as ar eference cation was performed. [NBu 4 ] + and (hypothetic) monomeric [Ga(dmap) 2 ] + have similar calculated cation volumes (0.379 vs.0 .376 nm 3 ,s ee Table S1 in the Supporting Information) and should thus have comparable diffusion constants.Amulticomponent analysis involving the reference signal at d( 1 H) = 3.12 ppm showed two additional dmap-based diffusion coefficients to the [NBu 4 ] + reference velocity of 2.69 10 À10 m 2 s À1 ( Figure S9), with one of them being higher (1.82 10 À9 m 2 s À1 )a nd the other being lower (6.93 10 À11 m 2 s À1 )t han the reference velocity.O ne may tentatively assign the first one to af ree dmap ligand and the second one to an aggregate.T hus,t he formation of the crystals is possibly as tepwise cyclooligomerisation of monomeric [Ga(dmap) 2 ] + units.T his conclusion is supported by electrospray-ionization mass spectra of solutions of 1 in oDFB,f or example,w ith the isotopic pattern of the signals centered at m/z = 425 for mononuclear [Ga(oDFB)(dmapÀH) 2 ] + as well as of di-and trinuclear complexes such as [Ga 2 (oDFB) 4 Them ain and hitherto unprecedented structural element of the pentacation 1 (hereafter: 1 5+ ;F igure 1a)i safivemembered Ga 5 ring that includes two dmap ligands attached to each gallium atom. With rather short GaÀGa distances of 248.75(9)-250.1(1) pm (average:2 49.5(6) pm), it forms an essentially planar pentagon.…”

“…The coordination chemistry of the Group-13-metal monocations Ga + and In + with ligands other than p-coordinating arenes [1] is still rather in its infancya nd that of Al + is even unknown. In principle,t he mixed-valence salts Ga + [GaX 4 ] À (X = Cl, Br, I) [2] appeared to be ideal starting materials for such chemistry.Y et, the introduction of neutral s-donors led to undesired redox chemistry (comproportionation or disproportionation). In this respect, the facile access to an In[SO 3 CF 3 ]s alt [3] was as tep ahead and allowed for the characterization of the first In + crown-ether complexes.…”

“…In this respect, the facile access to an In[SO 3 CF 3 ]s alt [3] was as tep ahead and allowed for the characterization of the first In + crown-ether complexes. [4] However,r elated chemistry with Ga + did not work and the only published compound which seemed likely to be asuitable starting material for coordination chemistry was the [Ga 2 Cp*] + cluster cation [5] -with the complication of providing one surplus equivalent of neutral GaCp* per used Ga + (Cp* = C 5 Me 5 ). Thes ubsequent facile access to arene complexes of In + and Ga + salts [6,7] with the non-reactive weakly coordinating anion (WCA) [8] [Al(OR F ) 4 ] À opened an ew starting point to interesting coordination chemistry with av ariety of s-donors including phosphines, [6,7] carbenes, [9] pyridines, [10] and also crown ethers.…”

“…[4] However,r elated chemistry with Ga + did not work and the only published compound which seemed likely to be asuitable starting material for coordination chemistry was the [Ga 2 Cp*] + cluster cation [5] -with the complication of providing one surplus equivalent of neutral GaCp* per used Ga + (Cp* = C 5 Me 5 ). Thes ubsequent facile access to arene complexes of In + and Ga + salts [6,7] with the non-reactive weakly coordinating anion (WCA) [8] [Al(OR F ) 4 ] À opened an ew starting point to interesting coordination chemistry with av ariety of s-donors including phosphines, [6,7] carbenes, [9] pyridines, [10] and also crown ethers. [11] In all of this,[ Al-(OR F ) 4 ] À was very helpful [12] for the elimination of cation-anion interactions and allowed for ap redictable reaction outcome.H owever,d ue to its considerable size (diameter 1.25 nm, V À = 0.76 nm 3 )and the pseudo-gas-phase conditions that the anion provides, [8,13] the overall charge of such coordination compounds was expected to be limited to + 1.…”

“…Thes ubsequent facile access to arene complexes of In + and Ga + salts [6,7] with the non-reactive weakly coordinating anion (WCA) [8] [Al(OR F ) 4 ] À opened an ew starting point to interesting coordination chemistry with av ariety of s-donors including phosphines, [6,7] carbenes, [9] pyridines, [10] and also crown ethers. [11] In all of this,[ Al-(OR F ) 4 ] À was very helpful [12] for the elimination of cation-anion interactions and allowed for ap redictable reaction outcome.H owever,d ue to its considerable size (diameter 1.25 nm, V À = 0.76 nm 3 )and the pseudo-gas-phase conditions that the anion provides, [8,13] the overall charge of such coordination compounds was expected to be limited to + 1. However,w hen changing to bidentate 2,2'-bipyridine (bipy) and phenanthroline (phen) as ligands,u nexpectedly,t he formation of indium-cluster-cation salts with planar triangles (for example,[ In 3 (bipy) 6 ] 3+ )a nd rhomboids (for example, [In 4 (phen) 6 ] 4+ )t hat both feature strong In-In bonding was observed.…”